The invention relates to a tubular photobioreactor and to the culturing of phototrophic macro- or microorganisms using a photobioreactor such as this.
Photobioreactors are used for the large-scale production of phototrophic organisms, e.g. cyanobacteria or microalgae, for example Spirulina, Chlorella, Chlamydomonas or Haematococcus. Microalgae of this type are able to convert light energy, CO2 and water into biomass. Photobioreactors of the first generation use sunlight as the light source. The reactors consist of large open tank units of a variety of designs, for example round tank units with diameters up to 45 m and rotating mixing arms. These reactors are generally made of concrete or plastics. Closed bioreactors are also used in various forms. Closed bioreactors can be plate bioreactors, tube bioreactors, (bubble) column bioreactors or tubular bioreactors. This type of reactor is made of transparent or translucent materials, such as glass or plastic.
Closed photobioreactors offer the advantage that the production of biomass can take place under controlled conditions and contamination of the culture can be suppressed. To improve the light input into the cultures by increasing the surface/volume ratio, tube or tubular photobioreactors are recommended, wherein to reduce the space requirement the tubes or tubing are wound helically round a cylindrical framework.
WO 2007/129327 A1 describes a photobioreactor that contains at least two transparent, spiral tubes, each wound round a cylindrical supporting framework, wherein the individual tube elements are joined together by their free ends. The tubes are preferably made of silicones. The reactor is illuminated by means of tubular lighting elements, which are arranged in the annular gaps between the individual spiral tube elements. Temperature control of the tube system is provided by a heat exchanger arranged outside of the helical arrangement. There is the problem here that the temperature conditions are nonuniform owing to the externally arranged heat exchanger and the different radiation intensity in the upper and lower portions of the reactor with the cylindrical-helical geometry. EP 239272 B1 describes a photobioreactor with a vertical core structure, which can be cylindrical or in the form of a cone. A transparent tube is wound helically round the outside of the core structure. Polyethylene is recommended as tube material. A heat exchanger arranged outside of the helical structure is recommended for temperature control. Illumination takes place externally by insolation. To increase the light intensity it is recommended to provide the inside of the core structure with a reflective coating or install artificial light sources in the core structure. This design has the drawbacks of variable radiation intensity with the cylindrical core structure, and inadequate temperature control with the external heat exchanger.
GB 2205581 A describes a photobioreactor with a cylindrical core structure or a core structure in the form of a truncated cone. One or two transparent plastic hoses are wound helically round the outside of this core structure. As an alternative, it is also possible for one hose to be arranged helically on the inside and one on the outside of the core structure. Transparent plastic or glass is recommended as hose material. Illumination is by sunlight or artificial light sources, which are fitted between the inside and outside of the core structure. No devices for attemperation of the culture medium are described. WO 2008/097845 A1 describes a photobioreactor with a cylindrical core structure, wherein helically wound hoses made of transparent plastic are arranged round the core structure. Temperature control is provided by a heat exchanger mounted on the inside of the core structure.
DE 29707043 U1 describes a photobioreactor with a transparent, tubular pipeline, filled with culture medium, encircling a carrying frame. To increase light supply, a light source is arranged inside the carrying frame, and a converging lens on the upper end of the carrying frame. To cool the circulating culture medium, it is recommended to provide air slots in the base of the carrying frame, for climate control of the internal space. U.S. Pat. No. 5,958,761 describes a cylindrical bioreactor for cultivation of algae, which is made of glass and comprises an outer cylinder with larger diameter, and an inner glass cylinder with smaller diameter. The inner cylinder is filled with the algal culture and is equipped with an agitator. To improve the light input, the outer cylinder is filled with a liquid whose refractive index is appropriate to the geometric ratio of inner and outer cylinders. This liquid can also serve as coolant. For further improvement of the light input it is recommended to place the glass cylinder in a mirrored parabolic trough. This has the drawback of unfavorable flow conditions in the inner cylinder, necessitating the installation of a complicated stirring unit.
Against this background, the problem was to provide a photobioreactor that is characterized, relative to the aforementioned prior art, in that the light input and temperature control are as uniform as possible throughout the reactor volume.